INTERFACIAL, PORE GEOMETRY AND SATURATION EFFECT ON COMPLEX RESISTIVITY OF SHALY SANDSTONE: DISPERSION AND LABORATORY INVESTIGATION

Electrical evaluation of reservoir rock needs to consider several factors that really describe subsurface condition. As confining pressure can cause pore space of the rock to collapse and rock properties also to change, it is needed to see details how much the effect of the pressure and also water saturation to electrical properties.

The investigations of electrical properties on shaly sandstones are the main focus in this work. The effects of pore geometries, confining pressure, and partial water saturation on electrical properties are investigated. The frequency of electrical measurement is between 1 Hz and 0.2 MHz.

It is indicated that interfacial and geometry change due to pressure easily is recognized by imaginary resistivity in low water saturation. This case reflects that confining pressure only influence small defect to pore geometry. Meanwhile in high water saturation, bulk volume conductivity is more dominant thus makes interfacial contribution become negligible. From petrographic analysis in this work it is found that only pore radius distribution has a good relationship with electrical dispersion.

The relaxation time and its distribution are estimated by simultaneous inversion of real and imaginary resistivity. The Cole-Cole model inversion is applied to obtain these parameters. For this purpose, it is used the integration of Lavenberg-Marquardt and Singular Value decomposition (SVD) in order to avoid singularity problems. The decreasing of relaxation time with the increasing of confining pressure is obtained and it reflects that internal surface area reduces.